1. Field of the Invention
The present invention relates, generally, to a pretreatment method of a magnesium alloy for electroplating the magnesium alloy, and more particularly, to a method of pretreating a magnesium alloy to electroplate the magnesium alloy so as to increase the usability of the magnesium alloy, having the highest specific strength among actually usable metals, through the development of a magnesium pretreatment process for the formation of a uniform copper (Cu) electroplating layer on the magnesium alloy.
2. Description of the Related Art
In general, a magnesium (Mg) alloy, which has the smallest weight among actually usable metals, has excellent specific strength (specific gravity/strength) and easy processability, and is thus widely used for parts of automobiles, computers, or information communication apparatuses. Although the magnesium alloy has been prepared mainly using a die casting process, an extrusion process, a rolling process, etc., it is recently formed using a thixo-molding process as an advanced technique by a combination of metal die casting and plastic injection molding. With the development of magnesium alloys able to undergo press forming, the demand thereof will increase more and more.
However, since the magnesium alloy has a relatively low standard potential among the actually usable metals, it may be easily oxidized in air, thus having corrosion resistance insufficient for use as an actually usable metal. Thus, great efforts have been made to increase the corrosion resistance of the magnesium alloy.
As surface treatment techniques for improvements in corrosion resistance of the magnesium alloy, a chromate treatment process has been widely conducted. However, the chromate treatment suffers because it discolors the surface of magnesium and a chromium compound of a solution used for chromate treatment causes environmental problems, and thus the use thereof is limited according to international environmental restrictions.
Therefore, although the development of non-chromate treatment has been actively conducted in recent years, such non-chromate treatment results in lower corrosion resistance and higher expense than those of the conventional chromate treatment.
In addition, an anodizing process has been developed, but it is limitedly used for internal parts where external appearance is not regarded as important or is applied only to under-films of coating or painting.
As the other surface treatment for an increase in corrosion resistance of the magnesium alloy, techniques for plating a surface of a magnesium alloy using a dry or wet process are proposed. However, the magnesium alloy is difficult to dry plate, including deposition plating in a vacuum, due to the high vapor pressure thereof.
The wet plating techniques are classified into a wet electroplating process using electrical energy, and an electroless plating process using a chemical reaction. As such, the electroless plating process is exemplified by an electroless nickel plating process. However, the electroless nickel plating process is disadvantageous because an electroless nickel plating solution has high production cost, and as well an electroless nickel plating layer should be double-, triple- or quadruple-formed while varying the amounts of phosphorus (P) to increase the corrosion resistance of magnesium.